Throughout the world, trolley buses are used for public and private transportation. Such buses utilize trolley poles which extend upwardly from the vehicle and contact a power transmission line which carries the power through the trolley pole to the vehicle where the power is provided to an electric motor used to move the vehicle. The power transmission lines which are constructed such that they may be contacted by the trolley are expensive to construct and particularly to maintain. A break or discontinuity in the line can cause a lack of power to all vehicles on that line which are electrically driven and repairs to damaged lines are costly and time consuming.
It is frequently the case that the trolley poles may become separated from the power transmission line or lines while the trolley vehicle is under movement. One way such a separation can occur is if the vehicle is being driven too quickly. Another way such a separation can occur is if there are faults or discontinuities in the overhead lines or if impacts to which the vehicles are subjected as by holes in a road, for example, are transmitted from the vehicle to the trolley poles.
When the trolley pole leaves the power transmission line, a cable connected between a retrieval pulley and the trolley pole is generally activated by the acceleration of the retrieval pulley and acts to pull the trolley pole downwardly such that it will not strike the power transmissions line after dewirement. Striking the power transmission line with a trolley pole after separation can cause serious damage to the lines and to the trolley poles.
The trolley pole retrieval is performed through a retrieval pulley which contains an inertia operated dog and a strong spring connected to the pulley. When the trolley pole dewires, it travels upwardly, a distance which activates the retrieval pulley by the inertia of the dog within in the pulley. The pulley then quickly pulls the cable and trolley pole downwardly and out of possible contact with the power lines.
Present pulleys, however, do not always work properly. The acceleration device may not be activated because the acceleration of the trolley pole in the vertical direction may not be great enough to timely activate the dog. If the dog is not timely activated, the trolley pole may travel upwardly a distance sufficient to strike the power lines which may then cause damage to the power lines.